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Questions tagged [speed-of-light]

The speed of light is a fundamental universal constant that marks the maximum speed at which energy and information can propagate. Its value is $299792458\frac{\mathrm{m}}{\mathrm{s}}$.

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How does one's view of the universe change as one approaches the speed of light?

I found an interesting and fun question at worldbuilding.stackexchange.com , that to my surprise, I don't find that easy to answer. I would like to quote here that question , but with a small ...
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Is there any time difference when we see distant a object? [duplicate]

I was just wondering that We see objects thru our eyes and light has to reach our eyes so that our brain can process that light. But then there must be a time difference between that object which I ...
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The time it takes light to reach different points on a plane

Imagine there is a light source which is held perpendicular to a plane. Is there a difference in the speed light hits a part of the plane?
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Speed of light in vacuum in non-inertial frame [duplicate]

Does the speed of light remains $c$ also in non-inertial frames? Or it changes from frame to frame?
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Where does energy come from when a laser bean exits lens at c?

Take a laser. Fire it at a lens. Prior to arrival at the lens the lasers pulsed beam’s speed is c. Traversing the lens it’s speed is less than c. Exiting the lens (and back to the vacuum) it’s speed ...
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Does Sagnac effect imply anisotropy of speed of light in this inertial frame of reference?

There seems to be a consensus that the one - way speed of light is anisotropic in a rotating frame of reference (Sagnac Effect). Imagine a rotating ring of infinitely large diameter. In accordance ...
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Question about Relativity and Proper Reference Frames [duplicate]

If your in a space ship moving at relativistic speeds in reference to an observer on Earth, time would have to be going slower on the space ship and faster on Earth. However, wouldn't the Earth be ...
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Does the fact that we can only measure the two-way speed of light undermine the axiom of invariance?

When we measure the speed of light we get the same answer in all directions. This is taken to undermine the aether or absolute motion hypothesis and give support to the proposal that the speed of ...
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Could harm due to spaghettification be mitigated by entering a black hole at almost the speed of light?

Say that we wanted to send a probe into a black hole, perhaps hoping to see if it's actually a wormhole that might transport the probe elsewhere. Upon approaching a black hole, the probe would ...
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Dielectric constant in terms of fundamental forces [duplicate]

How can one explain the slowing down of electromagnetic waves travelling in a medium using fundamental forces of nature like electromagnetism?
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Is the gravitational waves velocity also $c$, regardless the adopted inertial frame, and the source movement conditions? [duplicate]

The second postulate of STR was made exclusively for light (electromagnetic waves)? If gravitational waves also travel at velocity $c$, then are they obliged to fulfill this second postulate? Any ...
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Four-velocity vector of light

Please note that my question is not a duplicate, it is not about the speed of light, my question is only technical about the four velocity vector for light, its definedeness, value and constantness. ...
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Why is light affected by time dilations in space-time curvatures

My previous question on this site gave me an answer to what affects light - space warping or time warping. The answer is- both. But what now doesn't make sense to me is why light is affected by time ...
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How did Maxwell figure out the speed of light?

The Wiki article is about 2 graduate years of physics beyond my understanding. What is a good high-school rendition of his thought process: regarding his use of the "distributed capacitance and ...
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Would an observer going faster than the speed of light in a vacuum be able to observe photons that they emit? [closed]

If I could exceed the speed of light in a vacuum, would I be able to see photons that I previously emitted? Would this be theoretically possible?
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Cherenkov radiation relativistic correction

I have to write a paper on Cherenkov detection. And got a bit of an issue on the relativistic particle/recoil correction of the Cherenkov angle formula. Normaly $$cos( \theta_c) = \frac{1}{n\beta} $$...
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In what sense do photons exist?

In a photon's frame of reference travel is instantaneous, so presumably a photon cannot exist in its own frame of reference. I am not aware that a "beam" of photons interacts via gravity despite ...
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Why don't we see galaxies going back in time?

Galaxies 4,200 megaparsecs away will travel faster than the speed of light away from each other, so why don't we see those galaxies as Going back in time up to the moment of the big bang?
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Photons’ Speed (light speed) in vacuum [duplicate]

In a vacuum, are photons always traveling at 100% light speed? Can photons go any slower in vacuum? They have no mass which means they can go at 100% light speed, but do they have to?
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Does light travel faster in between Casimir plates?

Speed of light is in general $c/n$ where $n$ is a refractive index. But for example introducing two parallel plates with very small spatial separation will perturb the energy density of vacuum ...
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Speed of light as the maximum speed and movement course

Assuming we have 3 objects d,e,f moving on the same line while e is stationary, d is moving to the left at 'almost speed of light' and f is moving to the right at 'almost speed of light'. What is the ...
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1answer
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Journey away and back at close to the speed of light $c$

If a person drives away from a clock tower at a speed close to $c$ for one whole day, and then drives back to it at the same speed (for another day), what would he see during each of the journeys? I ...
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Are photons “born” travelling at the speed of light? In what manner do they propagate through space? [closed]

When an electron jumps from a high to a lower energy level and a photon is created, can the photon be detected from all vantage points or only from a discrete position? Does the atom nucleus cast a ...
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If a photon doesn't experience time, how can it have a frequency? [duplicate]

It is said that photons, moving at c, do not experience time. But then, if a photon doesn't experience time, how can it have a frequency?
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1answer
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How does temperature affect the refractive index of a vinegar?

I’m conducting an experiment on the relationship between temperature of vinegar and its refractive index.
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Why does Alfred Schild's time dilation experiment make sense?

From my understanding, the experiment is carried out between 2 observers under different gravitational acceleration. The first one fires 2 light pulses towards the second observer with a certain time ...
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1answer
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Thought experiment: if an observer can travel at the speed of light [closed]

What would the observer see if he could travel at the speed of light and shot a photon beam at the same time?
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1answer
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Speed of light dependent on source velocity in other medium [duplicate]

Does speed of light depends upon the velocity of source in a medium (like water) other than space? if yes, does the speed gets added up when the light source moves in direction of light?
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Spaceship A and Spaceship B move in opposite directions at half the speed of light, and A fires a laser at B, does the laser light reach Spaceship B? [closed]

This question has been bugging me for a week now! I believe it would, but logically, I feel like I'm missing something. Please give a full explanation.
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Do condensed-matter field theories with multiple fields generically have multiple speeds of sound?

It is well known that the low-energy physics of many non-relativistic condensed matter systems can be described by field theories that display emergent Lorentz symmetry. The heuristic way to figure ...
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1answer
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Light moving toward a moving observer's reference frame

The speed of light is supposed to be the same for all observers in an inertial frame, no matter the observer's speed. As a result, time slows down for observers moving quickly, and this explains why ...
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2answers
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Does Michelson-Morley experiment really disprove the existence of aether?

In the MM experiment, the speed of one light beam was supposed to slow down as it moved against the flow of aether, but when it bounced off the mirror, it would be moving in the opposite direction--...
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Dimensional grid of spatial coherence on earth of Pole Star radiation

One spot on earth receives a constant stream of stellar radiation: this is the North Pole where the Pole star radiation flows constantly. Given that a point source of light is considered to emit a ...
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Where does light get its speed from? [duplicate]

One source of light is, IIRC my high school physics, when an excited electron jumps back to its normal position. This jump generates a photon. How can an event like that shoot of a particle at the ...
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Can light be sped up to go 30 times fast than the speed of light in a medium?

Here's the link: https://sciencebulletin.org/researchers-develop-way-to-control-speed-of-light-send-it-backward/ Here's the line that makes no sense to me: Abouraddy and study co-author Esat Kondakci ...
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1answer
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When a valence electron is excited, how fast does it move from ground state to excited state?

Imagine an atom with a valence electron becomes excited and the electron moves to a higher orbital, is this transition between ground state and excited state at speed of light? If so, since it is not ...
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Explain the effects of differences in the velocities of electromagnetic waves to different substances

It's a GCSE specification point and I cannot find notes or answers on the internet. Can someone help me out?
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Problem with speed of light

I constructed a thought experiment, can't figure the answer. Two long (say $1\ \rm{km}$ long) railway cars are on parallel east-west tracks in a zero gravity environment. Each car has a light source ...
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Difficulty in understanding the three classes of events of light-cone

Recently I'm reading Chapter 2: Space and Time of A Brief History of Time. The paragraph that follows the light cone says: Given an event P, one can divide the other events in the universe into ...
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1answer
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How can the big bang be “observed”?

The Big Bang Observer is a proposed spacecraft to study gravitational waves. Especially the one that are thought to originate from the Big Bang. Question. How can we observe waves that has an origin ...
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Predictions followed from Fermat's Principle, according to Feynman

In his book Lectures on Physics, Feynman mentions two predictions followed from Fermat's Principle (chapter 26-4). 1) Given three media air (1), water (2) and glass (3) with indices measured against ...
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If the Earth is moving, then how is it possible to slow down light? [closed]

Given the following: Earth is spinning on its axis and also rotating around the sun. Light has no mass and is not affected by our moving atmosphere When we slow down light as is done here to a mere ...
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1answer
62 views

Speed of light and time dilation vs. mass and time dilation

Time slows for an observer the faster they come to the speed of light, large amounts of mass also also have an effect on time. How much mass would be needed to have the same effect on time as moving ...
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If a black hole is created from light, can this black hole then move at the speed of light?

Imagine we managed to squeeze light into a very tiny region of space so that the energy concentration at that point becomes a black hole. Can this black hole then move at the speed of light?
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1answer
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What motivated Einstein's postulate on the speed of light? [closed]

I know that there are several experiments (conducted after Einstein's formulation of Special Relativity) that confirm to some extend Einstein's postulate that nothing can travel faster than light. But ...
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2answers
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Is a finite lightspeed necessary for cause and effect to exist? [duplicate]

In this question I asked in somewhat unclear (unclear enough to be closed) fashion about the relationship between an infinite speed of light and the existence of cause and effect. In thís question, I ...
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0answers
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How does electricity travel near the speed of light if electrons drift at a snail pace? [duplicate]

I was in a reddit argument with someone who said electrons didn't flow at the speed of light in a circuit. Then he linked the Wikipedia page for drift velocity and defeated me in one fell swoop. Now, ...
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4answers
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Are cause and effect the same as in our Universe in a non-relativistic, Newtonian Universe in which the speed of light is infinite? [closed]

Suppose the Universe was non-relativistic so time and space would be independent of each other. In other words, both of them separately would be absolute and independent of an observer's motion (...
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1answer
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Energy of light

If a beam of light is travelling in full vacuum in same medium ,then , the energy of the light beam will decrease or not while moving through space ? The wavelength of the beam of light will change ...
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1answer
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What would the effects be on the world if light slowed down? [duplicate]

It would be really helpful if the effects were just given in a list form so I can research them. The reason why I am asking this is because I to write an essay regarding the effects of a change in a ...